Right Homonymous Hemianopia (RHH) is a type of vision loss where the same half of the visual field is absent in both eyes. The term “homonymous” means the loss occurs on the corresponding side, affecting the entire right visual field (everything to the right of the center point is unseen). This condition is not caused by a problem with the eye itself, but by damage to the neurological pathways or processing centers located in the brain. RHH is a consequence of an event that disrupts the brain’s ability to receive and interpret visual signals from the right side of the world.
Understanding the Visual Pathway and Mechanism
The visual pathway is a neurological route that begins at the retina and travels deep into the brain for processing. Light signals hit the retina, and the nerves from each eye travel toward the optic chiasm. This junction point is where visual information splits, ensuring signals related to one side of the visual world travel to the opposite side of the brain.
For the right visual field, light signals fall on the nasal half of the right retina and the temporal half of the left retina. These nerve fibers meet at the optic chiasm, where the nasal fibers from the right eye cross over to join the temporal fibers from the left eye. These combined fibers then form the left optic tract, which carries the complete picture of the right visual field.
The left optic tract relays visual information through the lateral geniculate nucleus to the left visual cortex, located in the occipital lobe. Damage to any part of this post-chiasmal pathway on the left side—the left optic tract, the left optic radiation (the fan-like projection of fibers), or the left visual cortex—will result in a loss of the right visual field. RHH is a direct neurological consequence of the brain injury being on the side opposite the visual field loss.
Recognizing the Visual Field Loss
Individuals with RHH experience a sudden, complete absence of vision to the right of their fixation point. The field loss respects the vertical midline precisely, creating a sharp boundary between seeing and non-seeing areas. While the loss may be total, it can sometimes be incomplete, manifesting as a right homonymous quadrantanopia (only the upper or lower right quarter is missing).
This field cut creates significant functional challenges, especially when navigating dynamic environments. Individuals may frequently bump into obstacles, trip over objects, or struggle to locate items on their right side. Reading ability is particularly impacted because the eyes cannot see the next word or easily find the beginning of the next line of text.
The condition is distinct from visual neglect, which is a problem of attention, not vision, where the person fails to acknowledge or respond to stimuli on the affected side. In RHH, the patient is aware of the missing visual field and typically attempts to compensate for it. However, the inability to quickly scan and process a scene on the right side slows reaction time and limits overall awareness of their surroundings.
Common Medical Events Leading to RHH
Damage to the retrochiasmal visual pathway causes RHH, and the most frequent underlying event is a stroke. Cerebral infarction or hemorrhage, particularly those affecting the posterior cerebral artery, account for the majority of cases (around 70% of diagnoses). The resulting lack of blood flow deprives the visual processing centers, especially the occipital lobe, of oxygen, leading to tissue damage.
Traumatic Brain Injury (TBI) is another common cause, often resulting from a severe blow to the head that causes contusions or shearing injuries to the optic radiation fibers. TBI is implicated in approximately 14% of cases. Brain tumors, which physically compress the visual pathways or the visual cortex, also contribute to RHH, accounting for about 11% of diagnoses.
Less frequent causes include brain infections, certain neurodegenerative diseases, or complications following neurosurgery. The specific location of the lesion along the left visual pathway dictates the characteristics of the resulting field cut. A sudden onset of RHH, such as from a stroke, is considered a medical emergency requiring immediate attention to address the underlying cause.
Practical Strategies for Living with RHH
Management of RHH focuses on maximizing the use of remaining vision through compensatory strategies and specialized aids. Systematic visual scanning training is an effective technique, teaching the individual to make larger, more purposeful eye and head movements into the blind right field. This training helps develop a new search pattern that is more efficient for exploring the environment and locating objects.
Specialized optical devices, such as spectacle-mounted prisms, can also assist with mobility. High-powered prisms, like Peli prisms, are fitted to the lens on the side of the field loss to shift images from the blind area into the seeing field. These prisms do not restore the lost vision but instead create a small area of peripheral awareness, often described as a “ghost image,” which acts as an alert for obstacles.
Vision Restoration Therapy (VRT) uses computer-based exercises to repeatedly stimulate the border between the seeing and blind visual fields. The goal of VRT is to potentially expand the functional visual field, though its efficacy remains a topic of ongoing research. A low-vision specialist or occupational therapist can provide tailored rehabilitation programs to help individuals adapt and improve their daily function.